Various medicated and unmedicated hydrogel dressings containing polyvinylpyrrolidone (PVP) are known.
Johnson & Johnson manufactures "Therapeutic Gel Dressing", which is a clear, semi-firm, cross-linked PVP/water gel, supported by an internal nonwoven web and a polyethylene backing, whose active surface is protected by a removable polyethylene release film. It is packaged in a shallow tray inside a foil peel-open pouch.
EPO Patent Application No. 83305770.6, published May 2, 1984, discloses a hydrogel absorbent wound dressing comprising a non-rigid layer of cross-linked polyvinylpyrrolidone (PVP) gel. The gel is preferably prepared by dissolving 15-25 percent by weight of PVP in water and cross-linking the PVP by means of ionizing radiation. A radiation level of between 1-5 MRADS, preferably from an electron beam, is used to effect cross-linking.
Said EPO patent application (a) teaches that it is desirable to add various medicaments to such a dressing, one preferred medicament being silver sulfadiazine (SSD) which is well known as an effective antibacterial agent, and (b) discloses a PVP gel dressing incorporating SSD.
When repeating the above-disclosed process, after the water dispersion of PVP/SSD was exposed to electron beam (E-Beam) radiation to form the gel, it was found that the color of the resulting medicated hydrogel dressings containing PVP/silver sulfadiazine (PVP/SSD) is an assortment of various colors (e.g. yellow, purple, green, brown, etc.). The shades of color in the gel change with aging, but remain different and mottled. This color problem is severe since E-Beam radiation is a necessary part of a preferred process of preparing the gel dressings, in which radiation is used to cross-link the PVP matrix and to transform the flowable dispersion of PVP/SSD into an insoluble, non-flowable gel. The variability of color of such a hydrogel wound dressing is not acceptable in medical applications since a medical practitioner would doubt the reliability of a non-standard, changeable product. The mottled product of many different colors, and shades of colors, while perfectly suitable from a utilitarian point of view, is esthetically unpleasing and completely contrary to what is considered acceptable in medical practice. Alternate methods, therefore, were sought to stabilize the color of the PVP/SSD gel in order to obtain a gel of uniform color.